1. Field of the Invention
The present invention relates to a printing apparatus and a calibration control method, and more specifically to controlling execution of a calibration that can cause a print characteristic of a printing apparatus to be a predetermined one.
2. Description of the Prior Art
A calibration for a printing apparatus, such as a printer, is normally performed in a form of updating of parameters used in image processing or other processing, such as output γ correction. In more concrete terms, these processing are generally executed by using lookup tables (also referred to as “LUTs”) and the calibration is done by updating the table data. To update the table data requires a series of processing including printing out of a predetermined image (e.g., a patch) by the printing apparatus to be calibrated and optically reading the printed image.
Ways in which the printer is used include a major way that the printer is used for performing printing based on print information, such as characters and images, sent from a host device such as a personal computer. Particularly, in recent years printers in an office or the like are often connected to a network to output print information generated by each of networked personal computers.
In such printing system, it is a most case that the calibration is performed as a procedure by the host device. When the calibration for γ correction LUT, which is caused according to a command by the user, is performed, the host device first sends print data to the printer to print out patches that corresponds to a predetermined number of densities (gradation values), respectively. These patches are read by a scanner and, based on a result of reading and data of the predetermined number of densities, table data for updating the γ correction LUT is generated.
The calibration data generated by the host device in this manner is used either by the host device or by the printing apparatus depending on a configuration of the printing system. More specifically, one of the configuration is that predetermined image processing including the γ correction is performed by the host device and then the processed data is sent to the printing apparatus, and another of the configuration is that the image processing is performed by the printing apparatus. In the latter case, the calibration data is downloaded to the printing apparatus.
On the other hand, a printing apparatus, which performs the calibration independently, is also known. This calibration can be executed relatively easily, especially with the printing apparatus of an electro-photographic system. More specifically, the calibration is performed by forming a predetermined number of patch toner images on a transfer drum, for example, without printing the patches on a print paper, reading the toner images with a preinstalled optical sensor and, based on a result of reading, generating calibration data.
Such calibration in the printing apparatus is automatically performed when components such as a photosensitive drum are replaced or when environmental parameters such as temperature and humidity change by more than a predetermined amount.
Above-described manners in which the calibration is performed, however, have respective following drawbacks. The calibration performed mainly under the control by the host device requires reading the printed patches with a scanner, which may impose a burden on the user.
Further, execution of such calibration controlled by the host device is often started with an instruction by the user. In such case, it is relatively difficult that the calibration is performed at an appropriate timing, and therefore, even when a result of the calibration performed before no longer matches the printing characteristic of the printer, the old result may continue to be used. As a result of this, print quality may be degraded.
On the other hand, the calibration performed independently by the printing apparatus forms the patches on, for example, the transfer drum, so that a large number of patches cannot be formed. The calibration therefore cannot be performed as precisely as that performed by the host device.
As described above, the calibration performed by the host device and the calibration performed by the printer have respective advantages and drawbacks.